This invention falls within the art of recombinant DNA and genetic engineering technology. It provides a new process for increasing expression of polypeptides in transformed prokaryotic host cells.
The advent of recombinant DNA technology has made feasible the production of large amounts of many polypeptides that would not otherwise be possible by conventional chemical synthetic methods. However, the biosynthesis of some polypeptides in genetically altered host cells has proven difficult, especially those of low molecular weight. The method most common in the art for achieving suitable expression of these small polypeptides has been to fuse a DNA sequence, coding for the polypeptide product of interest, onto the DNA sequence of a second polypeptide which is readily expressed. This type of construction allows for the expression of a final product which is therefore a fused combination of the two polypeptides. The fused expression product is then cleaved and the desired polypeptide product of interest is isolated from the resulting mixture.
Direct expression of small polypeptides as non-fused expression products is often difficult to obtain for reasons not specifically known. Among reasons proposed for low expression levels of small polypeptides are the possible rapid degradation of these small polypeptides by the host cell or an impaired transcriptional or translational efficiency of the underlying coding sequence. Regardless of the explanation, polypeptide derivatives of the present invention have higher levels of expression than polypeptides which are expressed without the benefit of the present invention.